(342b) Robust Saccharomyces Cerevisiae Strains For Ethanol Production

Industrial ethanol production requires organisms that can withstand the harsh environmental conditions of the fermentation process. Desired strain characteristics include resistance to high ethanol concentrations and temperature. The organism should also be tolerant of inhibitors which are commonly present in lignocellulosic hydrolysates. We have used a cytostat to develop strains with desired characteristics. The cytostat is a continuous culture method consisting of an automated flow cytometry system controlling a fresh medium feed pump and thus the cell number concentration. It has the advantage that the growing cell population can be exposed to precisely defined environmental conditions that determine the selection pressure during the cultivation process. One mutant, isolated after exposure to elevated acetic acid concentration, exhibited also tolerance to high ethanol concentrations as well as elevated temperature. Comparative genome hybridization using cDNA microarrays suggest that the mutant strain has a modified phospholipid metabolism as compared to the wild type strain. The growth and production kinetics of this haploid strain is comparable to the diploid ?Ethanol Red? strain that is commonly used in industrial ethanol processes. We are currently constructing a homozygous diploid version of the mutant strain which is expected to have even better growth and product formation characteristics. Using the current robust mutant as background, more mutations can be introduced through extended cytostat cultivation in order to increase the heat and ethanol tolerance.